The present invention relates to micromanipulators or micropositioners, and more particularly to a compact, remote controlled micromanipulator.
Parallelogram suspensions confer ease of construction, durability, and frictionless movements in micropositioning devices. However, displacements in the parallelogram suspensions move in arcs, so that an unwanted component of off-axis displacement or "cross-coupling error" exists that is orthogonal to the linear motion desired. Displacements in two dimensions will follow the surface of a sphere rather than a true plane--i.e., for horizontal motions, the position of the workpiece will fall below the horizontal plane at the extremes of displacement in either direction. Thus, when a microtool workpiece is moved either to or from the extremes in either horizontal axis, the displacement will move the microtool out of the narrow section of focus at the highest magnifications of the microscope. Since displacements must follow the tangent of the arc, motions between two axes are not truly orthogonal; vertical and horizontal actions will be mutually perpendicular only when the tangent of the spherical surface coincides with the horizontal plane. No exact correspondence exists between the change in the position of the microtool and the change in the settings on the remote micrometer, and so the device is not ideal for blind micropositioning.
Ball bearing slideways provide truly orthogonal motions, but they are subject to wear, effects of corrosion, and imperfections in manufacturing. Loads are always off-center with any kind of micromanipulator. Off-center loads create a moment that amplifies the force on the micromanipulator suspension, reducing the total load that can be borne. Thus a second problem with ball bearing suspensions is that the cantilever concentrates force and wear on the point contacts of a few ball bearings. For all kinds of suspensions, the existence of a large cantilever amplifies any cross-coupling errors and is thus both a potent source of pick-up for vibration during steady positioning and a source of unwanred oscillation during motions, i.e., acceleration of the workpiece. Thus it is desirable to reduce the size of the micromanipulator suspension, but this will exacerbate the cross-coupling errors of parallelogram suspensions because, when the dimensions of its lever arms are reduced to preserve the mechanical advantage, the curvatures of the parallelograms are increased.
Suspension of a load in a cantilever fashion creates a mechanical moment that favors rotation about a horizontal axis of the micromanipulator suspension. Horizontal stability in the parallelogram suspension of levers in the Huxley-style device is achieved by creating a counteracting moment, made large by increasing the vertical size of the device. The large size of these Huxley-style devices requires that they be placed alongside the microscope. They are too large to be stage mounted, as would be desired to reduce cantilevering of the workpiece.
A mechanical advantage is created by the levers in a Huxley-style device, but the length of the levers severely reduces the ability to rapidly advance a microtool, such rapid advancement being necessary to minimize damage to living cells during their impalement by the microtool. Rapid advancement can be achieved by including an additional piezoelectric device in the micromanipulator, but this remedy introduces its own problems: the piezoelectric device adds considerable mass to the micromanipulator, induces oscillations, is expensive, and introduces a source of electric noise into the experimental environment.
One advantage of the Huxley-style device is that the small size of its parallelogram suspension itself confers the large mechanical advantage in micromanipulation. Lever arms are integrated into the suspension, so that their action translates a large micrometer spindle displacement to a relatively small microtool displacement. The mechanical advantage, being created external to the suspension, reduces both the action and the load imposed upon the actuator, so that construction of precise actuators does not limit performance of the micromanipulator. Parallelogram suspensions have been devised in which the means of suspension confers no mechanical advantage, or actually decreases the mechanical advantage, of the micromanipulator's actuator elements. For example, De Fonbrune U.S. Pat. No. 1,987,733 describes a hydraulic micromanipulator that utilizes deformable boxes (FIGS. 11-14). The design provides only two-axis motion for a parallelogram suspension, and the force of displacement in the third axis is borne directly by the micromanipulator's actuator. In the De Fonbrune device, the site of action of the actuator element is placed between the fulcrum and the load so that the leverage created in the deformable box necessarily reduces the mechanical advantage of the suspension and amplifies the load imposed on the actuators.
Hall et al. U.S. Pat. No. 4,635,887 describes a micropositioner based upon a suspension that also appears to utilize a three-dimensional deformable box based on similar principles to those shown by De Fonbrune, although the displacements of the actuator are made equal to that of the deformable box. Since each actuator is directly linked to the base of each deformable parallelogram, no mechanical advantage is conferred by the suspension, and the load is directly borne by the actuator. Thus, the precision of manipulation requires construction of very precise actuators. Cross-coupling errors exists in either suspension, and they can be reduced only by increasing the size of the box to add unwanted bulk. The Hall et al. device is too large to place on a microscope stage, thereby requiring substantially cantilevering of the workpiece from an off-stage location.
Krueger U.S. Pat. No. 4,946,329, the substance of which is expressly incorporated herein by reference, discloses a remote controlled micromanipulator employing laterally intextensible metal bellows, connected by a flexible tubing of constant internal diameter, in both a micromaniputator and a remote controller. Variations of the length of one bellows is communicated to the other bellows by variations in hydraulic volume, as opposed to variations in hydraulic pressure. The Krueger micromanipulator permits making precise, reproducible microadjustments along three orthogonal axes in the position of a micromanipulator platform adapted to support a microtool for relative movement. The micromanipulator comprises a base plate, a platform, and means for operatively mounting the platform on the base plate for substantially orthogonal movement relative to the base plate. The mounting means includes, for each of the three orthogonal axes X, Y and Z, at least one pivotable bar, a displaceable lever arm fixedly secured to the bar for pivoting the bar, and an actuator bearing on the lever arm for displacing the lever arm relative to the base plate, and hence pivoting the bar to move the platform relative to the base plate. No means is provided, however, to compensate for the small cross-coupling errors which occur in one axis as a result of extreme displacements of the platform in either or both of the other axes. Accordingly, while the movement of the platform relative to the base plate is substantially orthogonal, it is not totally orthogonal. Further, while the preferred embodiments of the Krueger micromanipulator are compact, and can in particular instances be mounted on a microscope stage to minimize cantilevering of the microtool (thereby avoiding both an unwanted source of vibration and the limits on load bearing in large devices that can only be placed alongside the microscope), they are not as compact as desirable for easy mounting on a relatively small microscope stage.
Accordingly, an object of the present invention is to provide a durable, frictionless remote controlled micromanipulator having a parallelogram suspension.
Another object is to provide such a micromanipulator which has a compact suspension mountable on the state of a microscope.
A further object is to provide such a micromanipulator which gives rise to motions that are truly orthogonal and correspond faithfully to the settings on the micrometer spindles of the remote controller.
It is also an object of the present invention to provide such a micromanipulator wherein any vertical cross-coupling error that arises at the extremes of a parallelogram displacement of the two horizontal axes is hydraulically corrected by a remote controller.
It is another object to provide such a micromanipulator which is of simple and rugged construction, yet compact, stable and easy to construct, with good dynamic capability.